In this answer, the function is defined as
With(Math)f=(a,b,c,d)=>... (1)
However, f is not used in the function, so it seems fine to write
With(Math)(a,b,c,d)=>...
(the latter one's return value is also the function)
The point is that, you can't write
f = With(Math)(a,b,c,d)=>...
You either write (1) or
f = eval('With(Math)(a,b,c,d)=>...')
to make f be the function. Is that allowed?
With(Math)is just an import and not part of the function itself. \$\endgroup\$Thus, from math import* is not valid, but from math import*;gcd is.seems shows that it's allowed \$\endgroup\$